Hydrogen peroxide-alkali metal bicarbonate acidic bleaching process



United States Patent i 3,017,236 HYDROGEN PEROXIDE-ALKALI METAL BICAR-BQNATE ACIDIC BLEACHING PRDfiESS Neil J. Stalter, Wilmington, Del,assignor to E. I. (lit .lont tle Nemours and t'Jompan-y, Wilmington,Del, a corporation of Delaware No Drawing. Filed Aug. 14, 1959, Ser. No.833,710

2 Claims. (Cl. 8-111) This invention relates to the bleaching of varioussolid surfaces and to acidic bleaching solutions which are particularlyadapted to effectively bleach solid surfaces with a minimum of attendingdisadvantages.

Hydrogen peroxide solutions have heretofore been employed or proposedfor bleaching various solid surfaces such as those of wood, paperboard,paper and floor covering products such as linoleum and rubber tiles. Theuse of strongly alkaline peroxide solutions have almost invariably beenregarded as necessary for bleaching such surfaces. Alkaline solutionscontaining caustic soda, sodium silicate or other common non-volatilealk'alies have been most widely used. Usually, leaching is effected 'bydrying, e.g., by heating, such a solution on the surface to be bleached.This leaves a bleached surface coated with an objectionable grittyresidue of non-volatile alkali. Such residue can be removed by furtherprocessing at extra cost, e.g. by neutralization with an acid followedby lashing. The use of ammonia as the alkaline agent has been proposedto avoid formation of such alkaline residue, but hydrogen peroxidesolutions alkalized with ammonia do not give as effective bleaching asis generally desired. Furthermore, ammonia readily volatilizes with theformation of highly objectionable fumes.

It is an object of the invention to provide an improved peroxide methodfor bleaching such solid surfaces.

It is an additional object to provide an improved peroxide method forbleaching solid surfaces which avoids the use of strongly alkalineperoxide solutions, the formation of solid residues and objectionablefumes when the bleach solution is dried on the solid surfaces beingbleached. It is another object to provide bleaching solutions which areespecially Well suited for use in practicing the improved method of theinvention. Still further objects will be apparent from the followingdescription.

The objects of the invention are accomplished by the use of bleachingsolutions which are aqueous acidic solutions containing 10-50% by weighthydrogen peroxide (H 0 and an alkali metal bicarbonate at aconcentration of at least by weight, preferably -15% by weight. Solidsurfaces can simply be wet or coated uniformly with the bleachingsolution and the treated surfaces are then dried either at room orelevated temperatures.

Strong aqueous alkali bleaching solutions containing hydrogen peroxideand sufficient caustic soda to impart a relatively high pH have beensuccessfully used to bleach wood surfaces. Generally these solutions aresprayed on wood surfaces at room temperature and thereafter the surfacesare dried at elevated temperatures until the water has been completelyevaporated. A typical wood bleach contains:

Water gal 1 Caustic soda "lb... 1% Sodium silicate, 42 B oz 1 Lime oz 1H202 gals 3 These alkali bleaching solutions have also been applied withgood results to linoleum and similar hard-surface floor coveringmaterials, such as rubber tile, which are hardened by a heat curingtreatment that imparts a yellow discoloration. Unfortunately, alkalinesolutions damage Patented Jan. 16, 1962 ice certain types of linoleumand cause pitting. Additionally, bleaching solutions containing causticsoda leave a gritty residue on the bleached surface.

To overcome these disadvantages a bleaching solution containing ammoniumsalts has been developed which has about a neutral pH (pl-l 6.5-7.5).Salts such as ammouium carbonate, bicarbonate, sesquicarbonate,hartshorn salt (NH HCO -NH COONH and the like are volatile and whenapplied to linoleum and subjected to elevated temperatures give offammonia fumes. Ammonia fumes are irritating to personnel in theimmediate drying area and necessitate the use of special dryingcontrols. Another disadvantage of bleaching solutions containing theammonia salts is that of wetting; aqueous solutions containing ammon umbicarbonate, for instance, do not satisfactorily wet linoleum, althoughthis disadvantage is mitigated when a wetting agent is incorporated inthe solution.

it has been found that if an alkali metal bicarbonate, preferably sodiumbicarbonate, is used in slightly acidic peroxide bleaching solutions amore effective bleaching action is obtained when these solutions areapplied to linoleum, wood, paperboard and other solid surfacessusceptible to the bleachin action of peroxide. Using the preferredbicarbonate, NaHCO in an amount of at least 5% by weight together with10-50% hydrogen peroxide, a solution can be prepared which can beapplied to practically any linoleum surface without damage to thesurface. Furthermore, rapid assembly-line bleaching is possible becauseno noxious fumes are expelled when the treated surfaces are dried. Inaddition to excellent wetting characteristics, the solutionsunexpectedly result in a superior bleach both in terms of the initialbleach obtained and in showing less reversion of color after beingdried. In contrast to solutions containing caustic soda, the bleachingsolutions of the present invention are easily prepared since they areendothermic, not exothermic.

The concentration of the preferred bicarbonate should be at least 5% byweight and preferably 10-15% by weight, although higher concentrationsup to saturation concentration can be used.

The concentration of hydrogen peroxide in the bleaching compositiongenerally should be at least 10% of the weight of the composition.Higher concentrations up to about 50% are suitable and those in therange 20 to 40% are generally preferred because of their rapid effectivebleaching action, particularly when they also contain sodium bicarbonateat a concentration in the preferred range. The present compositions arereadily prepared simply by dissolving the required amount of the sodiumv bicarbonate compound in a commercial aqueous hydrogen peroxide, e.g.,of about 27 to 50% strength. No cooling is required during theirpreparation to prevent peroxide decomposition.

Aqueous bleaching solutions of the above type free of reagents otherthan hydrogen peroxide and the alkali metal bicarbonate compound arehighly effective for the present purpose and are generally preferred.They are weak acidic solutions having a pH of about 5.5-6.5.

Any of the solid surfaces heretofore known to respond to bleaching withhydrogen peroxide can in general be bleached by means of the presentcompositions. Illustrative are the surfaces of wood and wooden articles,paperboard, paper, fiber based acoustical tile such as wood pulp andbagasse tiles, and floor coverings such as linoleum, cork-tile,granulated cork pressed into sheets and rubber tile. These floorcovering products are generally prepared from compositions which containunsaturated materials such as drying oils or rubber which give surfacesa yellowish discoloration during the usual heat curing operation in themanufacture of such products. Such surfaces can be rapidly andeffectively bleached simply by wetting or coating them uniformly withthe present bleaching composition and permitting the wet surface to dryat ordinary or elevated temperatures.

Solutions were prepared as follows:

A. Ten parts of sodium bicarbonate (NaHCO were added to 90 parts of 35aqueous hydrogen peroxide plus 1 part of a Wetting agent, alkyl arylsodium sulfonate. This solution had a pH of 6.2.

B. Twenty parts of ammonium bicarbonate (NH4HCO3) were added to 80 partsof 35% aqueous hydrogen peroxide plus 1 part of wetting agent, alkylaryl sodium sulfonate. This solution had a pH of 6.4.

C. One hundred twenty-eight parts of water were added to 20 parts ofsodium hydroxide (NaOI-I), one-fifth of 1 part of calcium hydroxide(Ca(OH) 1 part of aque ous sodium silicate 42 B. and 1 part of the samewetting agent. This solution was then added to 450 parts of 35% aqueoushydrogen peroxide.

Each of solutions A, B and C were sponged onto separate sections of apiece of linoleum. An application of 0.12 lb./ sq. yd. was used. Thesamples were then dried for two minutes at 205-220 F., followed by arinse in cold tap water.

The samples bleached with solution A had a superior bleach to samplesbleached with solutions B and C. Solution A spread more easily andevenly on the linoleum than solution B, a decided advantage in theapplication of bleach solution on a production basis. Certain samples oflinoleum showed damage in the form of pitting when bleached withsolution C. There was no damage or pitting of samples bleached withsolution A.

The use of a Wetting agent in solution A is not necessary but ispreferred when used to bleach linoleum.

It was found that the use of solution B on a production basis created aproblem due to the NH fumes given off. The fumes were irritating topersonnel in the immediate area and special dryer control andconstruction was necessary to eliminate this problem.

Three solutions were prepared as follows:

A. Fifteen parts of solid sodium bicarbonate (NaHCO was dissolved in 85parts of 35% hydrogen peroxide. The resulting solution had a pH of 5.5.

B. Fifteen parts of solid ammonium bicarbonate (NI-I I-ICO was dissolvedin 85 parts of 35 hydrogen peroxide. The pH was 5.3.

C. A solution was prepared by adding 20 parts of caustic soda, 1 part of42 B. aqueous sodium silicate and 1 part of calcium hydroxide, to 130parts of water. One part of the resulting solution was then added to 3parts of 35% aqueous hydrogen peroxide to give the bleaching solution.

Each of solutions A, B and C was sprayed onto separate marked portionsof an unbleached hardboard sample. As much of each solution was sprayedon as would remain on the vertical surface. After spraying, the boardwas allowed to dry two minutes at room temperature and was then heatedin an oven at 140 F. for five minutes. The surfaces in each case werebleached from 19 to 29 G.E. brightness but there was no reversion ofbrightness on standing for one month at room temperature using solutionA. Reversion with solution B was. 20%.

Pine wood, was treated with each solution as above. Solutions A and Bboth bleached to about 45 GE. Wood bleached with NaHCO Formula A did notyellow or revert. in brightness on standing one month, whereas woodbleached with NH HCO formula yellowed up very noticeably. Formula Cbleached only to 40 G.E.

'Walnut veneer was treated in a similar manner. Formula A had lessyellowing after bleaching than B or C and was at a higher level ofbrightness.

In the above examples and throughout the specification, parts andpercentages are by weight unless indicated otherwise.

Pie-cleaning of the surfaces with soap and water, a solution of analkali or with an organic solvent which does not attack the surface,will permit employing hydrogen peroxide treating solutions free ofwetting agents. However, when a linoleum surface to be treated has notbeen pro-cleaned to remove mold lubricants, the addition of a wettingagent to the peroxide solution will be advantageous in order to obtainuniform treatment. In such cases Wetting agent concentrations rangingfrom about 0.55% are suitable.

The peroxide treating solution may also contain a thickening agent forincreasing its viscosity to facilitate uniform application and retentionof the solution. Suitable for this purpose are the water-soluble saltsof carboxymethyl cellulose and poly-acrylic acid.

The treatment with the peroxide solution is preferably effected bycoating the solution onto the surface of the linoleum product.Application or" the solution can be made by any of the usual methods forapplying liquids to surfaces, e.g., by dipping, spraying, sponging orbrushing, or by means of roller-type applicators, the latter beinggenerally preferred. The amount of solution to be applied will dependsomewhat on the particular surface being treated and the composition ofthe solution used. In general, application of from 0.002 to 0.01 poundof solution per square foot of surface will be satisfactory for mostpurposes.

Following application of the solution to the discolored surface, thesurface with the applied solution may be allowed to stand until thedesired result has been accomplished. However, it is preferred to employelevated temperatures to accelerate the decoloring action, particularlywhen continuous treatment is desired, as when treating continuous websof material. Heating to dry the applied peroxide solution on the surfaceis particularly effective. This can readily be accomplished usingradiant heaters, circulating hot air ovens or other conventional heatingmeans. Oven temperatures of from about 300 to 700 F. have been usedsuccessfully under conditions such that the surface temperature of theproduct ranged from about to 180 F. Care should, of course, be used toavoid temperature suthciently high to damage the product. Anotherelfective heating method is to contact the coated sur face with a metalsurface heated to a suitable temperature to effect rapid drying.

The invention provides a highly practical method for removing undesiredyellow discoloration from floor and wall covering products such aslinoleum and rubber tile. The present method is particularly welladapted for continuous operation in treating'materials of the abovetypes. which can be processed in continuous length, with consequentimportant savings in time and labor over the procedure previouslyemployed.

The embodiments of the invention in which an exclusive property orprivilege is claimed are defined as follows:

1. The method of bleaching a solid surface responsive to bleaching withhydrogen peroxide selected from the group consisting of linoleum, rubbertile, wood, fiber based acoustical tile, and paperboard, comprising thestep of coating said surface with an aqueous acidic bleaching solutionhaving a pH about 5.5 to 6.5 and containing at least 5% by weight of analkali metal bicarbonate and 10-50% by weight hydrogen peroxide.

2. The method of bleaching a solid surface responsive to bleaching withhydrogen peroxide selected from the group consisting of linoleum, rubbertile, wood, fiber based acoustical tile, and paperboard, comprising thestep of coating said surface with an aqueous acidic bleaching solutionhaving a pH about 5.5-65 and containing 10- 5 15% by weight of sodiumbicarbonate and 20-40% by 2,166,954 Kauffmann et a1 July 25, 1939 Weighthydrogen peroxide. 2,185,632 Hill et a1. J an. 2, 1940 2,203,589Baymiller June 4, 1940 References Cited m the file of thls patent 2,891819 Hawkinson July 7 1959 UNITED STATES PATENTS 5 2,960,382 Kelley eta1 Nov. 15, 1960 1,986,672 Bergman Jan. 1, 1935

1. THE METHOD OF BLECHING A SOLID SURFACE RESPONSIVE TO BLEACHING WITHHYDROGEN PEROXIDE SELECTED FROM THE GROUP CONSISTING OF LINOLEUM, RUBBERTILE, WOOD FIBER BASED ACOUSTICAL TILE, AND PAPERBOARD, COMPRISING THESTEP OF COATING SAID SURFACE WITH AN AQUEOUS ACIDIC BLEACHING SOLUTIONHAVING A PH ABOUT 5.5 TO 6.5 AND CONTAINING AT LEAST 5% BY WEIGHT OF ANALKALI METAL BICARBONATE AND 10-50% BY WEIGHT HYDROGEN PEROXIDE.